1. Field of the Invention
The present invention relates to a color display device and a method for driving the device.
A plasma display panel (PDP) is used as a television display device having a large screen. Since the PDP is also suitable for a public display for its good viewability, a plurality of PDPs are often combined to be used as a multiscreen.
2. Description of the Prior Art
In display of an AC type PDP having display electrodes covered with a dielectric layer, line-sequential addressing is performed for setting wall voltage of cells in accordance with display data, followed by sustaining process in which a sustaining voltage pulse is applied to the cells. In other words, the addressing process determines light or non-light, and the sustaining process generates display discharge at the number of times in accordance with the luminance of display. Since the PDP cell is basically a binary light emission element, an image having different luminance for each pixel cannot be displayed in one addressing process. Therefore, a frame to be displayed is divided into a plurality of subframes, and the addressing process and the sustaining process are performed for each subframe. In the case of an interlace display, each of fields constituting the frame is divided into subfields. As a simple example, a subframe division number K is set to three, and a ratio of luminance weights (i.e., light emission quantities) is set to 1:2:4 for total three sustaining processes as shown in FIG. 12A. An eight-level gradation display having gradation levels 0-7 can be performed by selecting light or non-light for the first subframe (SF1), the second subframe (SF2) and the third subframe (SF3) as shown in FIG. 12B. A color display can be performed by applying this gradation display to R (red), G (green) and B (blue) cells.
In the above-mentioned gradation display by the subframe division, the number of gradation levels that can be displayed increases as the division number K increases. However, since the addressing process of one screen is necessary for each subframe, the number of times of addressing that can be performed during a period that is determined by a frame rate (usually 1/30 seconds) is limited. Therefore, the subframe division is limited. Actually, the upper limit is 256 gradation levels for the division into eight subframes.
Concerning this problem, Japanese unexamined patent publication No. 2000-100333 discloses a method for increasing the number of gradation levels by assigning a plurality of cells having the same color to one pixel. Namely, one pixel is displayed by total six cells including two each of R, G and B colors. Since the light emission quantity is changed by lighting one or both of the two cells, the light emission quantity can be set to three kinds including non-light by one addressing process.
However, in the plasma display panel disclosed in the above-mentioned publication, characteristics of all cells are the same concerning drive control, and electrodes are arranged equally in all cells. Namely, as a common structure in which one pixel is displayed by three cells including one each of R, G and B colors, electrodes are arranged so as to control light or non-light of each cell. Therefore, the number of electrodes increases as cells having the same color corresponding to one pixel increases. Thus, a driving device (an integrated circuit module) having output terminals covering the number is necessary.